As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKE-OFF IT WAS NOTED THAT THE ENGINE WAS NOT DEVELOPING FULL POWER. WHEN THE POWER SETTING WAS REDUCED TO ESTABLISH THE AIRCRAFT ON A DOWNWIND LEG A LOW FREQUENCY ENGINE VIBRATION WAS NOTED. A 1/4 INCH DIA CHIP WAS FOUND MISSING ON THE CIRCUMFERENCE OF THE EXHAUST VALVE OF NR 3 CYLINDER.